The petroleum industry has used clamping mechanisms in a variety of applications. One such application is for cross-well seismic surveying. Another use is for well casing/cement bond diagnostics. The vibratory source in borehole surveying requires a rigid clamp to couple seismic energy. At the same time, the seismic receiver also requires a clamp for good coupling. Seismic imaging technology has uses in the analysis of nuclear waste storage, repository sites, and for the study of geological features. A clamp is a mechanism that secures body A to body B. A rigid clamp does not allow for relative motion between A and B. For example, a vise is a clamp that secures body A (the work piece) to body B (the table); however, it may not be stiff because of the movable vise jaw. A collet is a clamp that is fairly stiff and self-centering for circular cross-section work pieces; however, it requires a wedging action that causes the "clamping force" to vary with the relative displacement between the work piece (both A) and the collet housing (body B).
In robotics, gripping and placement of objects is frequently required. The gripping mechanism is at times required to grab odd shaped objects. In particular, a robotic end effector used for positioning a workpiece during a machining operation would require a rigid clamp.
In the past, wedging techniques have been developed for clamps. These types of clamps have been difficult to set and release particularly due to the sensitivity of such clamps to external forces acting on the clamp; for example, a collet or a camming-type clamp.
In an effort to improve on the clamping devices and techniques of the prior art, the apparatus of the present invention has been developed with an eye toward providing a clamp that has a simple structure to build and, at the same time, operates reliably to support or grasp an object. Specifically, with an eye toward downhole applications, where it is recognized that the well casing has surface irregularities and a certain amount of out-of-roundness, the clamp of the present invention has been designed to compensate for such irregularities and out-of-roundness to obtain a substantial grip on such casing. To accomplish such an object, the clamp mechanism has been developed with a self-centering feature. A further object of the invention is to eliminate the prior designs' reliance on a wedging action or compliant mechanisms and to provide a simple structure that presents more consistent and constant holding force.